Method of making porous rubber and compositions employed therein



April 7, 1942. M. M. HARRISON ETAL 2,278,441

METHOD OF MAKING POROUS RUBBER AND COMPOSITION EMPLOYED THEREIN Filed July 29, 1938 Zz'Y-L/E' n' faz-25 2 75mm-z 2 7 7- aaafsan 10u15 FEDu/a' Patented Apr'. 7,

METHOD F MAKING POBOUS RUBBER. AND

' COMPOSITIONS EMPIDYED-THERElN Marion M. Harrison ne una r. Gouna, Anon,

Goodric j Ohio, assig'nors to' The B; 1".

pany, New York; N. Y., a corporation o! York h ACom- New ` Application July 2s, 193s, semi No. 222,034

(el. 11s-53) i '13 Claims.

I'he invention relates to the manufacture of porous rubber products and has for its chief objects the provision of simple, economical, and ef- .flcient methods of lmanufacturing sponge and other porous rubber products directly from liquid rubber latex and the elimination ofthe principal ,difficulties and 'disadvantages which have been encountered in the commercial practice of methods heretofore proposed for utilizing latex in the direct manufacture of porous spongy rubber products. A

In the process of the present invention, liquid rubber latex is expanded to a porous state by means of an expanding agent incorporated in the latex, and the expanded latex is then permanently set in the expanded porous state as by coagulation and vulcanization of the expanded latex.

We have discovered that butane is a very eiiective agent for expandinglatex and that mixtures" of i latex and butane exhibit certain extraordinary and entirely unexpected characteristics which have been utilized to lprovide what is believed to be the simplest. most practical, and generally most satisfactory method which has .been devised for producing sponge rubber from latex. The invention contemplates both the novel mixture of latex and butane and the method employing such mixtures in the manufacture of sponge rubber.'

y are thereafter changed to a condition of higher temperature or lowered pressure, or both, the butane will tend to increase in volume and expand the latex to a porous state. Surprisingly,-

however, a mixture oi latex and' butane in the bulk may b'e exposed to ordinary room conditions of temperature and pressure for long periods without any appreciable change taking place. The latex is not expanded appreeiably and only insignificant quantities of butane are lost. Exr pension of the latex may be effected by heating themixture of latex and butane to elevated temperatures or by subjecting the mixture to vacuum but such expediente, although entirely feasible. involve some undesirable features and have not been adopted for commercial use. It has been found, however, that if a mixture of latexv and butane atv room temperature and pressure is merely spread in a thin lm, the butane will expand the latex and produce an excellent uniform porous structure which may be set 'permanently by coagulation and vulcanization.

It has iurtherbeen found that liquid butane at a temperature around 0 C. may be stirred into .latex at room temperature and pressure without substantial loss o! the-butane upon mixture with the much warmer latex. It is therefore unnecessary tocool the latex or to utilize pressure in charging the latex with butane. The

liquid butane ordinarily would be expected toboil immediately upon contact with the much warmer latex at a temperature approximately 25 C. above the boiling point of butane, and the amazing fact thatsuch boiling is negligible and that the liquid butane may be mixed with latex at room temperature and stored i'ory long periods in a closed container under ordinary conditions of temperature and pressure has not been satisfactorily explained. Such mixtures have been kept in a corked bottle for several months and then caused to expand simply by iiowing the composition from the bottle onto a sloping surface.

These discoveries have been utilized in developing the present invention to provide a process in which the low-boiling, highly volatile, butane is added to latex in the bulk to provide a mixture which may be handled under ordinary room conditions of temperature and pressure without appreciable change taking place, but which can be caused to expand merely by spreading the mixture in a thin nlm to produce an excellent porous latex structure.

To further indicate the manner of practicing the invention, a -speciiic example illustrative of 'a preferred embodiment of the invention will be set forth in considerable detail, although it is to be understood that the invention is by no meanslimited to such details, nor tothe particular embodiment described.

To manufacture a sponge rubber product such i as "Age-Rite White." and 0.4 part oi potassium by thorough but gentle stirring. The'mixture then is poured promptly into conventional molds which preferably are pre-treated with any wellknown mold lubricant, and the molds are closed as such aging appears to have some-beneficial effect not yet understood.

To the prepared latex composition at room temperature (about 25 C.), liquid butane at a temperature around C. is slowly added with gentle stirring comparable to stirring cream into coffee, the butane being added for example in the proportion of c. c. of butane to each 100 parts of rubber, which is approximately 7.5% butane by weight based on the rubber content of the latex. As butane is an oily hydrocarbon immiscible withvwater, the latex should contain sufficient emulsifying agents to emulsify the butane, or, as usually proves to be more satisfactory, the emulsifying agent should be mixed with and allowed to stand at room temperature until -the expanded latex is completely coagulated,

which ordinarily will require about twenty to thirty minutes depending of course upon the character and quantity o f delayed coagulant employed. The rubber then is vulcanized as by'immersing the filled molds for a suitable time in f water heated to an appropriate temperature. For the specific example hereinabove set forth, im-

the butane before it is added to the latex. 2

The latex-butane mixture then is spread in a thin film as by flowing the mixture down a slightly inclined surface where, after a few minutes time, the latex will be expanded to a porous structure which can be scraped of! the surface and poured or spread as hereinafter indicated. In commercial operations, a quantity of the latexbutane mixture may be placedin a horizontal, substantially closed cylinder and the cylinder ro- 'tated slowly to spread the mixture repeatedly upon the cylinder walls in` thin lrns and so progressively to expand the entire bulk to the desired porous state. As the latex-butane mixture hereinabove described will multiply in volume about 750% upon expanding, the cylinder should contain initially only a, small quantity of the unexpanded mixture. Simple and convenient apparatus may be'provided by -using a metal drum having a removable and replaceable head and placing the drum-horizontally on rollers to effect the required rotation. The headof the drum 4should have a small aperture in the center to permit escape of gas and prevent accumulation of pressure within the `,drum during the expanding operation. In a-typical case, about two gallons oi' the prepared latex-butane mixture should `be placed in such a d'rurnof about thirty gallons capacity and the drum should be rotated at a slow speed of about four or flverevolutions per minute for-about an hour, at room ,temperature of course, to eilect maximum expansion of the.

latex. The drum will then be found to contain about fifteen gallons of pourable, spreadable latex in a highly uniform porous state.

'Ihere is then added to the expanded latex 5.0 parts by weight (to each 100 parts of rubber) of zinc carbonate to'provide the zinc necessary for vulcanization. There is next addeda quantity 'of any well-known delayed coagulant" adequate to mersing the filled mold for-seventyflve minutes in water heated to the boiling point by steady admission of steam will effect satisfactory vulcanization of the rubber. The molds are then opened and the vulcanized spongy ruLber product isv removed, washed, and dried, all according yto conventional'procedures.

'I'he resulting product is ahigh quality sponge rubber article having fine pores of substantially uniform character, and having a density of about .14 i i 'I'he room in which the process is carried out should be well .ventilated and precautions should be taken -to avoid all sparks and flames in order to prevent explosion of the Vhighly 'inflammable butane.

The exemplary process hereinabove described is outlined in the accompanying drawing which sets forth, in flow-sheet style, the principal steps embodied in' the particular processv described. It should be understood, however, that the process described and outlined in the drawing represents only one embodiment of the invention chosen for purposes of illustration and that the -inventionis capable of embodiment in other described.

eifect coagulation of the expanded latex aiter a I solutionv and mixed well with the expanded latex Instead of molding the expanded latex to produce a sponge rubber article asv hereinabove described, it may be utilized in anyother manner in whichsuch a spreadable pourable expanded latex has been used. For example, it may be poured or spread upon fabric or other sheet ma.-v terial or applied to other surfaces and then coagulated and vulcanized to provide porous coatings upon such surfaces. All such spongy articles and coatings may be lvulcanized either to the soft rubber state. or to the hard rubber state. Molded slabs of such porous rubber are excellent heat insulators. The invention promises to find wide use in the manufacture of seat cushions. mattresses, cushion pads of various types, and similar spongy articles. process adapts it to commercial manufacturing conditions and insures low manufacturing costs.

Numerous modifications' and variations in de.- tails of the invention as hereinabove` described may be made without.V departing from the 4spirit vand scope of the discovery. Thus, in addition to the variations already indicated, iso-butane having a boiling point reported as from -11 C. to 10.6 C. may be used as the expanding agent instead of normal butane. The unmodified term butane in the claims accordingly includes both normal butane and iso-butane. 'I'he quantity of butane used may be` varied widely with respect to the latex. `Any well known vulcanizing, compounding. stabilizing, conditioning and preserving agents maybe substituted for those specifically mentioned. Other -well known coagulating agents active either at ordinary temperatures 'I'he extreme simplicity of the after the elapse of time or at elevated or lowered temperatures either immediately or after elapse of time may be employed in place of theammonium chloride. Sodium silico fluoride, for example, is one well known excellent coagulating agent. The liquid rubber latex of course may be either a natural rubber latex or an artificially produced dispersion of rubber or rubber-like material. Although not essential, the latex may be cooled when the liquid butane is added to reduce somewhat the slight loss of butane which may occur. Instead'of adding the butane in liquid form to the latex, gaseous butane may be admitted under a pressure of approximately 22 pounds per square inch to a closed chamber containing latex, preferably at a lowered temperature approximating theboiling point of butane. More simply, gaseous butane may be bubbled throughlatex maintained at a temperature near C. All such methods effect a substantial impregnation of the latex with butane to produce a mixture useful in the manufacture of porous rubber. All such `modiilcations and variations are within the scope ofv the invention as defined by the appended claims unless otherwise specically indicated.

We claim:

l. A composition of matter comprising iiqui rubber latex and butane. y

product which comprises adding butane to latex under conditions inhibiting expansion of the' latex by the'butane, altering the conditions to permit expansion of the latex by the butane to produce an expanded, porous latex structure, and setting the expanded latex in permanently porous form.`

5. The method of making avporous rubber productwhich comprises adding butane to latex in the bulk, spreading the latex-butane mixture in a thin film to permit expansion oi'vthe latex by the butane to produce an expanded, porous latex structure, and setting the expanded latex is not effective tov expand latex in the bulk, and

in permanently porous form.

6.*The method of making a porous rubber product which comprises adding liquid butane at atmospheric pressure to latex at a temperature substantially higher than the atmospheric presy sure boiling point of the butane, spreading the mixture in a thin nlm to effect expansion of the latex to porous form, and setting the expanded latex in permanently porous form.

7. The method of mai-:ing a porous rubber product which comprises adding liquid butane at atmospheric pressure to latex at a tempera-ture substantially higher than the atmospheric pressure boiling point of the butane to provide a latex composition permeated with butane but which is stable for appreciable periods under ordinary conditions of temperature and pressure, and then altering the conditions to permit expansion of the latex by the butane to produce an expanded, porous latex structure, and setting the expanded latex in permanently porous form.

8. The method of making a porous rubber product which .comprises admixing liquid butane into liquid rubber latex in the presence of an emulsifying agent to provide a latex-butane mixture which is stable for appreciable periods under ordinary conditions of temperature and pressure so long as the mixture is maintained Yin bulk form, and thereafter reducing the bulk of the mixture to eiect expansion of the latex by the maintained in bulk form, and thereafter reducing the bulk of the mixture by spreading it in a thin lm to` eifect expansion of the latex by the butane to produce an expanded, porous latex structure.

10. The method of making a porous rubber product which comprises admixing' liquid butane into liquid rubber latex in the presence of an emulsifying agent to provide a latex-butane mixture which is stable for appreciable periods under ordinary conditions so long as the mixture is maintained in bulk form, and thereafter reducing the lbulk of the mixture by placing a relatively small quantity of the mixture in a container of relatively large capacity and rotating the container-to spread the mixture in thin iilms upon the container walls, whereby the latex is expanded to porous form.

11. The method .which comprises admixing butane with liquid rubber latex in the presence of an emulsifying agent, placing a relatively small quantity of the resulting composition in a container of relatively large capacity, and rotating the container whereby the composition is spread in thin films on the container walls and is expanded by the butane to produce a porous latex product.

12. The method which comprisesv admixing with latex in the bulk an expanding agent which thereafter spreading the composition in a thin nlm `to reduce the bulk'of the composition and thereby to induce vexpansion of the latex to a porous state.

13. The method of making a molded sponge rubber article which comprises stirring liquid butane at atmospheric pressure into liquid rubber latex in the presence of anemulsifying agent, 

